Multilayer electronics assembly and method for embedding electrical circuit components within a three dimensional module

ABSTRACT

A multilayer electronics assembly and associated method of manufacture are provided. The multilayer electronics assembly includes a plurality of stacked substrate layers. Each of the substrate layers is fusion bonded to at least an adjacent one of the plurality of substrate layers. A first discrete electrical circuit component is bonded to a first layer of the plurality of layers. A bonding material is interposed between the discrete electrical circuit component and the first layer. The bonding material has a reflow temperature at which the bonding material becomes flowable that is higher than a fusion bonding temperature of the substrate layers.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.13/758,843, filed Feb. 4, 2013, which claims the benefit of the priorfiled U.S. Provisional Application No. 61/596,652, filed Feb. 8, 2012,the content of each application being incorporated herein by referencein its entirety.

BACKGROUND Technical Field

The present disclosure relates to a multilayer electronics assembly andan associated method of manufacture.

Description of the Related Art

Conventionally, multilayer printed circuit boards using epoxy fiberglass(FR4), fluoropolymer composites (such as polytetrafluoroethylene, PTFE),or mixed dielectric (MDk, a combination of FR4 and PTFE) have been usedto route signals to components that are mounted on the surface of amultilayer structure. These multilayer printed circuit boards mostcommonly include traces that are etched copper as one means of routingsignals to components. For these circuits, resistors can bescreen-printed or etched. These multilayer printed circuit boardassemblies can be used in a variety of applications including, amongothers, RF and power electronics modules. As one example, thesetechnologies can form multifunction modules (MFM) which carry monolithicmicrowave integrated circuits (MMICs) on their surface.

In another conventional method, multilayer integrated circuits andmicrowave, multifunction modules, are constructed of multiple layers offluoropolymer composite substrates that are bonded together into amultilayer structure by utilizing a fusion bonding process. Thecomposite substrate material can be PTFE filled with glass fibers andceramic. These multilayer structures may include thin film resistorsthat are screen printed or etched into the individual layers prior tothe fusion process. For example, resistors can be etched into thinnickel phosphate films adjacent to copper layers, using a method that issimilar to copper etching.

Certain discrete electrical circuit components, for example discretedevices, such as passive discrete resistors, capacitors, magneticdevices, and active semiconductor devices, are not merely thin filmscreated by etching or screen printing. Instead, these discrete devicesare attached to a substrate with, for example, a solder paste thatcannot withstand the heat and/or pressure of the fusion bonding process.To incorporate such discrete electrical circuit components into amultilayer integrated assembly, the conventional method includes formingcavities in individual substrate layers, attaching the discreteelectrical circuit components in the cavities, and applying a polymerbonding film layer as a separate, post-fusion bonding step. For example,U.S. Pat. No. 6,009,677 to Logothetis et al. and U.S. Pat. No. 6,395,374to McAndrews et al. describe a process for manufacturing a multilayerstructure of fusion bonded fluoropolymer composite substrates in whichdiscrete electrical circuit components are attached post-bonding withincavities formed in the multilayer structure, and then covered with afilm bonded layer.

BRIEF SUMMARY

It has been observed that a multilayer electronics assembly can beachieved by using a bonding material to attach the discrete componentsthat: (1) has a processing temperature for attaching discrete componentsthat is lower than a glass transition temperature of the layers of themultilayer structure to which the discrete components are attached, and(2) goes through a state transition following processing to attach thediscrete components that results in requiring a significantly highertemperature post-processing in order to change back to a liquid,flowable, or pliable state, in which the post-processing statetransition temperature is also substantially higher than the fusionbonding temperature of the substrate layers of the multilayerelectronics assembly.

A multilayer electronics assembly may be summarized as including aplurality of stacked substrate layers, each of the plurality ofsubstrate layers fusion bonded to at least an adjacent one of theplurality of substrate layers; a first discrete electrical circuitcomponent bonded to a first layer of the plurality of layers; and abonding material interposed between the discrete electrical circuitcomponent and the first layer, the bonding material having a reflowtemperature at which the bonding material becomes flowable that ishigher than a fusion bonding temperature of the substrate layers.

The multilayer electronics assembly may further include a seconddiscrete electrical circuit component bonded to a second layer of theplurality of layers. The plurality of substrate layers may be stacked ina first direction, and the first discrete electrical component overlapsthe second discrete electrical component in the first direction. Theplurality of substrate layers may be stacked in a first direction, andthe first discrete electrical circuit component may be positionedbetween adjacent layers of the plurality of stacked substrate layers.The substrate layers may include a fluoropolymer composite. The bondingmaterial may be nanosilver sintered solder. The bonding material may bea transient liquid phase bonded alloy. The first discrete electricalcircuit component may be one of a passive discrete resistor, acapacitor, a magnetic device, and an active semiconductor device.

A multilayer electronics module may be summarized as including a threedimensional, unitary block of a first material having a reflow point, atwhich the bonding material becomes flowable, at a first temperature; anda plurality of discrete electrical circuit components embedded withinthe unitary block, each of the plurality of discrete electrical circuitcomponents bonded to the block by a second material having a meltingpoint at a second temperature that is higher than the first temperature.

The unitary block may include an exterior surface defined by a topsurface, a bottom surface, and a plurality of side surfaces, and thefirst material may completely surround at least a first one of theplurality of discrete electrical components such that the first materialis positioned between all sides of the first one of the plurality ofdiscrete electrical components and any point on the exterior surface ofthe unitary block. The first material may not directly contact the firstone of the plurality of discrete electrical components. The plurality ofdiscrete electrical circuit components may include a first discreteelectrical circuit component, a second discrete electrical circuitcomponent, and a third discrete electrical circuit component, the firstdiscrete electrical circuit component overlaps the second discreteelectrical circuit component in a first direction, and the firstdiscrete electrical circuit component overlaps the third discreteelectrical circuit component in a second direction that is perpendicularto the first direction. The first material may be a fluoropolymercomposite. The second material may be nanosilver sintered solder. Thefirst material may be a transient liquid phase bonded alloy. Theplurality of discrete electrical circuit components may be selected froma group consisting of a passive discrete resistor, a capacitor, amagnetic device, and an active semiconductor device.

A multifunction module may be summarized as including a primarysubstrate, a power semiconductor die bonded to the primary substrate; aplurality of secondary substrates stacked on the primary substrate andfusion bonded to each other, a first discrete electrical circuitcomponent bonded to a first substrate of the plurality of secondarysubstrates with a first material that has a first melting point that ishigher than a fusion bonding temperature of the substrate layers, and asecond discrete electrical circuit component bonded to a secondsubstrate of the plurality of secondary substrates with a secondmaterial that has a second melting point that is higher than the fusionbonding temperature of the substrate layers; and an active electroniccomponent attached to an external surface of one of the plurality ofsecondary substrates that is positioned furthest from the primarysubstrate. The first material may be the same as the second material.

A method of embedding discrete electrical circuit components within amultilayer module may be summarized as attaching a first discreteelectrical circuit component to a first substrate via a first bondingmaterial that is initially flowable at a first temperature therebycausing the bonding material to go through a state transition such that,once the bonding material hardens, the bonding material will not returnto a flowable state until a second temperature, which is higher than thefirst temperature, is reached, the first temperature is lower than afusion bonding temperature of the first substrate, and the secondtemperature is higher than the fusion bonding temperature of the firstsubstrate; attaching a second discrete electrical circuit component to asecond substrate via the bonding material; and fusion bonding the firstsubstrate to the second substrate.

Attaching the first discrete electrical circuit component to the firstsubstrate may include nanosilver sintering the first discrete electricalcircuit component to the first substrate. Attaching the first discreteelectrical circuit component to the first substrate may includetransient liquid phase bonding the first discrete electrical circuitcomponent to the first substrate.

A multilayer electronics assembly may be summarized as including aplurality of substrate layers stacked in first direction, each of theplurality of substrate layers bonded to at least an adjacent one of theplurality of substrate layers; a bonding material having an initialtransition temperature at which the bonding material becomes initiallyflowable, and a subsequent transition temperature at which the bondingmaterial subsequently becomes flowable after hardening following theinitially becoming flowable, the initial transition temperature lowerthan the subsequent transition temperature; a first discrete electricalcircuit component bonded to a first layer of the plurality of layerswith a bonding material, the bonding material; and a second discreteelectrical circuit component bonded to a second layer of the pluralityof layers with the bonding material, the second discrete electricalcomponent overlaps the first discrete electrical component in the firstdirection.

In the multilayer electronics assembly, the bonding material is a solidimmediately prior to the subsequent transition temperature beingreached. The substrate layers may include at least one of epoxyfiberglass and polyamide. The bonding material may be nanosilversintered solder or a transient liquid phase bonded alloy. The firstdiscrete electrical circuit component may be one of a passive discreteresistor, a capacitor, a magnetic device, and an active semiconductordevice.

A method of embedding discrete electrical circuit components within amultilayer module is summarized as including attaching a first discreteelectrical circuit component to a first substrate via a bonding materialat a first temperature thereby causing the bonding material to gothrough a state transition such that the bonding material will notreturn to a flowable state until a second temperature, which is higherthan the first temperature, is reached; attaching a second substrate tothe first substrate; and attaching a second discrete electrical circuitcomponent to the second substrate via the bonding material at the firsttemperature.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, identical reference numbers identify similar elementsor acts. The sizes and relative positions of elements in the drawingsare not necessarily drawn to scale. For example, the shapes of variouselements and angles are not drawn to scale, and some of these elementsare arbitrarily enlarged and positioned to improve drawing legibility.Further, the particular shapes of the elements as drawn, are notintended to convey any information regarding the actual shape of theparticular elements, and have been solely selected for ease ofrecognition in the drawings.

FIG. 1A is an exploded, pictorial view of a multilayer electronicsassembly.

FIG. 1B is a pictorial view of the multilayer electronics assembly ofFIG. 1A in a partially assembled state.

FIG. 2 is a side view of a multilayer electronics assembly prior tofusion bonding.

FIGS. 3A-3F illustrate several sequential acts for embedding discreteelectrical circuit components within a multilayer module.

FIG. 4 illustrates one example temperature profile for nanosilversintering.

FIG. 5 illustrates a flow chart of several sequential acts for embeddingdiscrete electrical circuit components within a multilayer module.

DETAILED DESCRIPTION I. System Overview

In the following description, certain specific details are set forth inorder to provide a thorough understanding of various disclosedembodiments. However, one skilled in the relevant art will recognizethat embodiments may be practiced without one or more of these specificdetails, or with other methods, components, materials, etc. In otherinstances, well-known structures associated with electrical circuits,including discrete electrical components such discrete electroniccomponents, and/or printed circuit boards including insulativesubstrates and conductive traces and vias have not been shown ordescribed in detail to avoid unnecessarily obscuring descriptions of theembodiments.

Unless the context requires otherwise, throughout the specification andclaims which follow, the word “comprise” and variations thereof, suchas, “comprises” and “comprising” are to be construed in an open,inclusive sense, that is as “including, but not limited to.”

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment. Thus, the appearances of the phrases “in one embodiment” or“in an embodiment” in various places throughout this specification arenot necessarily all referring to the same embodiment. Furthermore, theparticular features, structures, or characteristics may be combined inany suitable manner in one or more embodiments.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural referents unless the contentclearly dictates otherwise. It should also be noted that the term “or”is generally employed in its broadest sense, that is as meaning “and/or”unless the content clearly dictates otherwise.

The headings and Abstract of the Disclosure provided herein are forconvenience only and do not interpret the scope or meaning of theembodiments.

For the purposes of the present disclosure, the phrase “discreteelectrical circuit component” is intended to include discrete electricalcircuit components, including electronic components which are formedseparately from the printed circuit board and are thus selectivelyplaceable thereon or attachable thereof, and exclude thin film elementsthat are formed as part of forming the printed circuit board as screenprinted or etched directly into the traces of individual layers of amultilayer module (i.e. resistors that are etched into thin nickelphosphate films adjacent to copper layers, using a method that issimilar to copper etching).

As discussed above, conventional fusion bonded multilayer modules do notsupport embedding discrete electrical circuit components within themodule due to the inability of conventional device attachment methods tosurvive the temperature/pressure of fusion bonding. Instead, theconventional fusion bonding method includes forming cavities inindividual substrate layers, attaching the discrete electrical circuitcomponents in the cavities, and applying a polymer bonding film layer asa separate, post-fusion bonding step. This technique adds process steps,does not provide as good of protection for the discrete electricalcircuit components (particularly bare semiconductor die), and does notsupport as high of density of packaging in a three dimensional module.For example, only one discrete electrical circuit component can beplaced in a given horizontal (X-Y) location in a cavity, and devicescannot be stacked or overlap within the vertical (Z) dimension. Further,discrete electrical circuit components that are placed within cavitiesand then covered by an additional layer or layers cannot be electricallyconnected to the additional covering layer(s) unless additionalpost-fusion drilling or etching and plating is performed. In addition,the immunity to moisture ingress is limited by the integrity of thebonding film that is applied as a post-fusion step, instead of theintegrity of the unitary structure formed through fusion bonding.

The techniques of the present disclosure may provide improved packagingdensity and performance for electronic products, particularly formicrowave and power applications, when compared with the conventionalmethod. Specifically, the present disclosure describes a method forembedding discrete electrical circuit components, both active andpassive devices, three dimensionally within a fusion bonded multilayermodule. The resulting assembly achieves higher density and potentiallybetter performance due to reduced circuit parasitics, particularly forcircuits operating with high frequency, high di/dt, or dv/dt, comparedto non-integrated (e.g., surface mount, non-three dimensional)solutions.

As discussed in greater detail below, the discrete electrical circuitcomponents are attached using a device attachment method that has aprocess temperature compatible with discrete electrical circuitcomponents and the composite module fusion bonding temperature and are-melt temperature significantly above the composite module fusionbonding temperature. For example, a bonding material can be used thathas an initial transition temperature at which the bonding materialbecomes initially flowable, and a subsequent transition temperature atwhich the bonding material subsequently becomes flowable after hardeningfollowing initially becoming flowable. The initial transitiontemperature is lower than the subsequent transition temperature.

For example, as discussed in greater detail below, a device attachmenttechnique such as nanosilver sintering or transient liquid phase bondingare used to attach the discrete electrical circuit components to thesubstrate layers prior to fusion bonding. Each of these device attachmethods shares the characteristic that: (1) the process temperature isless than the substrate and discrete electrical circuit component ratedtemperatures for soldering (or alternative device attachment) and (2)the resulting bonding material has a significantly higher re-melt orreflow temperature than conventional solder and is greater than thecomposite substrate fusion temperature.

II. Hardware

FIGS. 1A and 1B are simplified representations of a multilayerelectronics assembly incorporated into a device according to oneexample. FIG. 1A shows exploded view of the major sub-assemblies of thedevice. The subassemblies include a multilayer electronics assembly 10,base substrate 20, and a heat-sink 30.

In this example, the base substrate 20 can be an aluminum nitride (AlN)direct bonded copper (DBC) substrate that includes a plurality ofconductive traces 22 (such as, for example, copper traces) on a topsurface thereof, a plurality of bare die 24 (such as, for example, powerMetal Oxide Semiconductor Field Effect Transistors, MOSFETs) bonded tothe top surface thereof, and a plurality of interconnecting posts 26extending from the top surface thereof.

The multilayer electronics assembly 10 includes discrete electricalcircuit components embedded therein in three dimensions. As discussed ingreater detail below, the multilayer electronics assembly 10 is formedby a fusion bonding process in which the discrete electrical circuitcomponents are bonded to the internal layers of the assembly prior tofusion bonding. A plurality of cavities 14 are formed on a bottomsurface of the multilayer electronics assembly 10 to accommodate thebare die 24 on the substrate 20. As shown in FIG. 1B, the multilayerelectronics assembly 10 also includes a plurality of cavities 16 on atop surface thereof to accommodate higher profile parts that areattached using surface mount technology. Thus, active components can beattached on a top side, at 10 b, of the multilayer electronics assembly10 or on a bottom side, at 10 a, of the multilayer electronics assembly10.

In one example, the bare die 24 on the substrate 20 are attached to themultilayer electronics assembly 10 with a nanosilver sinteringtechnique. For example, a nanosilver sintered solder paste can be usedwithin the cavities 14. In this example, nanosilver sintering isachieved with a temperature profile that ramps to approximately 180° C.to bake out the binder within the nanosilver paste and then raises thetemperature to approximately 280° C. for 10 minutes to sinter thenanosilver particles. The resulting interfacial “solder” joint has asignificantly lower thermal and electrical resistance than conventionallead or lead-free solder, improved integrity in the presence of repeatedthermal cycling induced stress, and, a solder joint that will not‘reflow’ until >900° C. This latter property allows post-processing thatpotentially includes exposure to the fusion bonding process of themultilayer electronics assembly 10 and post-process soldering oftop-side components without reflow of the power semiconductor solderjoints.

As noted above, the discrete electrical circuit components of themultilayer electronics assembly 10 are bonded to the internal layers ofthe assembly prior to fusion bonding. FIG. 2 shows a more detailed sideview of an example multilayer electronics assembly prior to fusionbonding.

Starting from the bottom of the assembly, a first layer 300 is aheat-sink. In this example, the heat-sink 300 can be cast to support avariety of thermal interface options, e.g., solid with mounting holes310 for conduction, channels for liquid (not shown), or pin fin/slottedfins (not shown) for cooling air.

A second layer is a base layer 200 shown in this example with copper oneach side. As with the base substrate 20, the base layer 200 can be analuminum nitride (AlN) direct bonded copper (DBC) substrate. The baselayer 200 can be attached to the heat-sink 300 by epoxy, solder(nanosilver sintered solder, or, if the heat-sink is attached after thefusion bonding process, standard solder), or, if the base layer 200 isnot clad with copper on the side facing the heat sink, fusion bonding(either separately or as a single act for the whole assembly). Aplurality of power semiconductor dies 510, such as MOSFETs, are placedwith either side down to the base layer 200 in order to facilitate anoptimal circuit layout. As discussed in greater detail below, thesesemiconductor dies 510 can be attached to the base layer 200 and amultilayer electronics assembly 100 using a device attachment techniquesuch as nanosilver sintering or transient liquid phase bonding.

The multilayer electronics assembly 100 is arranged above the base layer200. A first (lowest) layer 110 of the multilayer electronics assembly100 can act as a spacer and interconnect layer between top and bottomsides of the semiconductor dies 510. A plurality of layers 120, 130,140, 150, 160, 170, and 180 are stacked above the first layer 110. Theselayers can include discrete electronic components 520, 530, and 560bonded thereto by a device attachment technique such as nanosilversintering or transient liquid phase bonding. The discrete electroniccomponents 520 can be, for example, passive discrete resistors,capacitors, a magnetic device, or an active semiconductor device.Surface mount techniques can be used to add further components 540 and550 topside. The device can include a power interconnect 600, which canbe, for example, a flat copper ribbon interconnect for supplying powerto the device.

The dielectric properties of a fluoropolymer composite such aspolytetrafluoroethylene (PTFE) filled with glass and ceramic cancontribute to a multilayer structure including power electronics that iswell suited for radiofrequency applications. However, as noted above,the scope of the present disclosure is not limited to the use of PTFE asa substrate material.

Likewise, the present disclosure is not solely limited to fusion bondedassemblies. For example, it is also possible to create a multilayermodule with three dimensionally embedded discrete electrical circuitcomponents by utilizing layers made of printed wire board (PWB)materials such as using epoxy fiberglass (FR4) or polyamide. The layerscan be assembled using, for example a controlled adhesive, such as areinforcement material pre-impregnated with a resin matrix (a“prepreg”), can be directly assembled with nanosilver sintering, can bedirectly assembled via transient liquid phase bonding, or can beassembled using a combination of these techniques. In the case of directassembly with nanosilver sintering or transient liquid phase bonding,the layers could be spaced a sufficient amount to allow outgassingduring processing. An encapsulant could then be used to seal gapsbetween layers, if environmental exposure is a concern.

Nanosilver sintering or transient liquid phase bonding makes it possibleto attach devices to an individual layer and then subsequently sinterone layer to another without worrying about the previously attacheddevices becoming detached due to the heat required to attach subsequentdevices. For example, the bonding material (in the case of nanosilversintering or transient liquid phase bonding) for the devices goesthrough a state transition following processing to attach the devicesthat results in requiring a significantly higher temperaturepost-processing in order to change back to a liquid, flowable, orpliable state. This post-processing state transition temperature is alsosubstantially higher than the temperature required to initially attachthe devices. The resulting structure would include discrete electricalcircuit components that are three dimensionally embedded within amultilayer module without requiring the creation of cavities in thelayers post assembly.

III. Method of Manufacture

Several acts for embedding discrete electrical circuit components threedimensionally within a multilayer module are hereinafter described withreferences to FIGS. 3A-3F, 4, and 5.

In a first act, 800 in FIG. 5, the individual layers of the multilayerelectronics assembly are fabricated. For example, FIG. 3A illustratesthe layers 110 and 200. A layer 110 can be a fluoropolymer composite(such as polytetrafluoroethylene, PTFE) filled with glass and ceramic.The base layer 200 includes a conductor 410, such as copper on eitherside. As noted above, the base layer 200 can be a direct bond coppersubstrate formed of an AlN board. For layers where nanosilver sinteringis to be used for device attachment, the surface final finish can begold or silver. As shown in FIG. 3A, the individual layers can includevias 420, that allow for connectivity between layers.

In a second act, 810 in FIG. 5, discrete electrical circuit componentsare attached to the individual layers. For example, FIG. 3B illustratesdiscrete electrical circuit components 520, which can be passiveelements such as resistors and capacitors, or small signal activedevices, attached to an individual layer 130. The discrete electricalcircuit components 520 can be bonded to the layer 130 using nanosilversintering or transient liquid phase bonding. One example of transientliquid phase bonding is described in “Highly Reliable Nickel-TinTransient Liquid Phase Bonding Technology for High TemperatureOperational Power Electronics in Electrified Vehicles”, by Sang WonYoon, Satoshi Yasuda, Michael D. Glover, Koji Shiozaki. An example ofnanosilver sintering is described in International Publication No. WO2005/079353.

In the present example, the discrete electrical circuit components 520are attached to the individual layer 130 by nanosilver sintering, usingthe temperature profile shown in FIG. 4. In this example, no pressure isused for die attachment of components that are smaller than 10 mm×10 mm.

In a third act, 820 in FIG. 5, a subassembly is assembled for bonding.For example, FIG. 3C illustrates the assembly of layers 110 and 120 withthe base layer 200 and the power semiconductor die 510. Theinterconnecting posts 430 assist with the alignment of the layers. Inthis example, nanosilver solder paste is silkscreened onto each oflayers 110, 120, and 200. For example, a 50 μm thick layer of nanosilveris silkscreened on and allowed to air dry. Then a 10 μm layer ofnanosilver is applied, the power semiconductor die 510 are put in place,and the layers 200, 110, and 120 are arranged in preparation for thesintering process. Layer 120 is shown with vent holes 122 drilled aboveand or around the periphery of the power semiconductor die 510. Thesevent holes 122 allow the solvents and binder in the nanosilver solderpaste to escape during the sintering process.

Next, as shown at 830 in FIG. 5, the elements of the subassembly arebonded together. For example, as shown in FIG. 3D, pressure is appliedwith plates 710 and 720. Plate 720 includes vent holes 722 aligned withthe vent holes 122 in the layer 120. The pressure is applied to ensurethat solvents are baked out from underneath the die and the vent holes722 allow the gas to escape. In this example, approximately 3-5 MPa isused for the nanosilver sintering process when die of greater than 10mm×10 mm are used. The profile in this example is essentially the sameas shown in FIG. 4, except that pressure is applied at the 180° C., 10minute portion of the profile (and as/if needed during ramp up to 180°C.). Pressure can then be removed before taking up to 275/300° C.

Next, as shown at 840 in FIG. 5, the layers are assembled for fusionbonding. For example, as shown in FIG. 3E, the remaining layers 130,140, 150, 160, 170, and 180 are stacked along with the sub-assembly oflayers 110, 120, and 200 that are now sintered together. These layersare then fusion bonded (850, FIG. 5). Fusion bonding is typicallyaccomplished in an autoclave or hydraulic press by heating substratelayers past the PTFE composite melting point while simultaneouslyapplying a determined amount of pressure, preferably mechanically,isostatically, or a combination of both. The alignment of layers istypically secured by a precision fixture with a plurality of pins (suchas the interconnecting posts 430 in the present example), preferablythree to eight but possibly more, to stabilize flow as the PTFE resinchanges state to a viscous liquid and adjacent layers fuse underpressure. Depending on the size of the stack being bonded, the pinarrangement for alignment of the stack is preferably triangular orrectangular. The pins themselves are preferably round, square,rectangular, oval, or diamond-shaped, but may have other shapes.

Because the discrete electrical circuit components 510, 520, and 560were attached to the respective layers by nanosilver sintering ortransient liquid phase bonding, the discrete electrical circuitcomponents 510, 520, and 560 are able to remain bonded to the conductivepaths in the module during the fusion bonding process. For example, themelting temperature of an alloy formed by transient liquid phase bondingand the melting point of the bond formed nanosilver sintering far exceedthe temperature required to achieve a PTFE composite melting point forfusion bonding. The resulting three dimensional, unitary, multilayerelectronics module 1000 is depicted in FIG. 3F. The multilayerelectronics module 1000 includes a plurality of discrete electricalcircuit components 510, 520, and 560 embedded three dimensionally withinthe fusion bonded block. Unlike conventional multilayer, fusion bondedmodules, the module 1000 in FIG. 3F, includes discrete electricalcircuit components stacked in layers such that the discrete electricalcircuit components overlap within the vertical dimension. In addition,the discrete electrical circuit components are electrically connected tosurrounding layers without the need for additional post-fusion drillingand plating. Further, immunity to moisture ingress is supported by theintegrity of the unitary structure formed through fusion bonding.

After fusion bonding is performed, the heat-sink and the top-sidesurface mount components are attached (860, FIG. 5). For example, asshown in FIG. 3F, the heat-sink 300 is attached below the multilayerelectronics module 1000, and top-side surface mount technology parts 540and 550 are attached to a top surface of the multilayer electronicsmodule 1000. A low thermal resistance can be achieved by fusion bondingthe heat-sink 300 to the base layer 200, if the base layer 200 is notclad with copper on the side facing the heat sink. In one example, thiscan be achieved as part of the fusion bonding act discussed withreference to FIG. 3E. In this case, the heat-sink 300 can be designedwith a ‘web’ matrix between modules to facilitate cutting the modulesapart. This cutting may be achieved with water jet cutting. In anotherexample, the heat-sink 300 can be AlSiC cast in sectional modules heldtogether by the Al skin so that only the Al skin needs to be cut. Inanother example, the heat-sink 300 could be soldered to the assemblyillustrated in FIG. 3E, or bonded thereto.

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, U.S. patent applicationpublications, U.S. patent applications, foreign patent applications andnon-patent publications referred to in this specification areincorporated herein by reference, in their entirety. Aspects of theembodiments can be modified, if necessary to employ concepts of thevarious patents, applications and publications to provide yet furtherembodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

1. A method of embedding discrete electrical circuit components within amultilayer module, comprising: attaching a first discrete electricalcircuit component to a first substrate via a bonding material that isinitially flowable at a first temperature thereby causing the bondingmaterial to go through a state transition such that, once the bondingmaterial hardens, the bonding material will not return to a flowablestate until a second temperature, which is higher than the firsttemperature, is reached, the first temperature is lower than a fusionbonding temperature of the first substrate, and the second temperatureis higher than the fusion bonding temperature of the first substrate;attaching a second discrete electrical circuit component to a secondsubstrate via the bonding material; and fusion bonding the firstsubstrate to the second substrate.
 2. The method of claim 1, whereinattaching the first discrete electrical circuit component to the firstsubstrate includes nanosilver sintering the first discrete electricalcircuit component to the first substrate.
 3. The method of claim 1,wherein attaching the first discrete electrical circuit component to thefirst substrate includes transient liquid phase bonding the firstdiscrete electrical circuit component to the first substrate.
 4. Themethod of claim 1, further comprising: prior to fusion bonding the firstsubstrate to the second substrate, stacking a plurality of substratelayers, which include the first substrate and the second substrate, in astacking direction with the first discrete electrical circuit componentoverlapping the second discrete electrical circuit component in thestacking direction.
 5. The method of claim 1, further comprising: priorto fusion bonding the first substrate to the second substrate, stackinga plurality of substrate layers, which include the first substrate andthe second substrate, in a stacking direction with the first discreteelectrical circuit component positioned between adjacent layers of theplurality of stacked substrate layers.
 6. The method of claim 1, whereinthe first discrete electrical circuit component is one of a passivediscrete resistor, a capacitor, a magnetic device, and an activesemiconductor device.
 7. The method of claim 1, further comprising:prior to fusion bonding the first substrate to the second substrate,stacking a plurality of substrate layers, which include the firstsubstrate and the second substrate, in a stacking direction; and fusionbonding the plurality of substrate layers together to carry out thefusion bonding of the first substrate to the second substrate and toform a unitary block of substrate material.
 8. The method of claim 7,wherein fusion bonding the plurality of substrate layers togetherincludes enclosing the first discrete electrical circuit componentwithin the unitary block of substrate material.
 9. The method of claim7, wherein fusion bonding the plurality of substrate layers togetherincludes enclosing the first discrete electrical circuit componentwithin the unitary block of substrate material without the unitary blockof substrate material directly contacting the first discrete electricalcircuit component.
 10. The method of claim 7, wherein fusion bonding theplurality of substrate layers together includes enclosing each of thefirst discrete electrical circuit component and the second discreteelectrical circuit component within the unitary block of substratematerial.
 11. The method of claim 7, wherein fusion bonding theplurality of substrate layers together includes enclosing each of thefirst discrete electrical circuit component and the second discreteelectrical circuit component within the unitary block of substratematerial without the unitary block of substrate material directlycontacting the first discrete electrical circuit component or the seconddiscrete electrical circuit component.
 12. The method of claim 7,wherein stacking the plurality of substrate layers includes manipulatingthe first substrate with the first discrete electrical circuit componentattached thereto and the second substrate with the second discreteelectrical circuit component attached thereto relative to each other.13. The method of claim 12, wherein, while manipulating the firstsubstrate and the second substrate relative to each other, the firstdiscrete electrical circuit component remains fixedly attached to thefirst substrate by the bonding material in a hardened state and thesecond discrete electrical circuit component remains fixedly attached tothe second substrate by the bonding material in a hardened state. 14.The method of claim 1, further comprising: attaching a third discreteelectrical circuit component to the first substrate via the bondingmaterial to overlap with the first discrete electrical component in adirection that is perpendicular to a thickness direction of themultilayer module.
 15. A method of embedding discrete electrical circuitcomponents within a multilayer module, comprising: providing a primarysubstrate; die bonding a power semiconductor to the primary substrate;attaching a first discrete electrical circuit component to one of aplurality of secondary substrates with a bonding material that has amelting point that is higher than a fusion bonding temperature of thesecondary substrates; attaching a second discrete electrical circuitcomponent to another one of the plurality of secondary substrates withthe bonding material; thereafter stacking the secondary substrateshaving the first and second discrete electrical circuit componentsattached thereto on the primary substrate to form a stack of secondarysubstrates on the primary substrate; fusion bonding the stack ofsecondary substrates to form a unitary block of secondary substratematerial with the first discrete electrical circuit component and thesecond discrete electrical circuit component enclosed therein; and afterfusion bonding the stack of secondary substrates, attaching an activeelectrical circuit component to an external surface of the unitary blockof secondary substrate material.
 16. The method of claim 15, whereinattaching the first discrete electrical circuit component to thesecondary substrate includes nanosilver sintering the first discreteelectrical circuit component to the secondary substrate or transientliquid phase bonding the first discrete electrical circuit component tothe secondary substrate.
 17. The method of claim 15, further comprising:prior to fusion bonding the stack of secondary substrates, attaching theprimary substrate to one of the plurality of secondary substrates toform a subassembly such that, when the stack of secondary substrates aresubsequently fusion bonded together, the primary substrate is fixedlyattached to the unitary block of secondary substrate material.
 18. Themethod of claim 15, wherein stacking the plurality of secondarysubstrates having the first and second discrete electrical circuitcomponents attached thereto on the primary substrate includes arrangingthe first discrete electrical circuit component to overlap with thesecond discrete electrical circuit component in a direction of thestacking.
 19. A method of embedding discrete electrical circuitcomponents within a multilayer module, comprising: attaching a firstdiscrete electrical circuit component to a first substrate via a bondingmaterial that is initially flowable at a first temperature therebycausing the bonding material to go through a state transition such that,after the boding material hardens, the bonding material will not returnto a flowable state until a second temperature, which is higher than thefirst temperature, is reached; attaching a second substrate to the firstsubstrate; and attaching a second discrete electrical circuit componentto the second substrate via the bonding material at the firsttemperature.